Throughout a long and distinguished career stretching over six decades Fred Hoyle sought to answer some of the biggest questions in science. How did the Universe originate? How did life begin? What are the eventual fates of planets, stars and galaxies? More often than not he discovered answers to such questions in the most unsuspected places.

Hoyle believed that, as a general rule, solutions to major unsolved problems had to be sought by exploring radical hypotheses, whilst at the same time not deviating from well-attested scientific tools and methods. For if such solutions did indeed lie in the realms of orthodox theory upon which everyone agreed, they would either have been discovered already, or they would be trivial.

Hoyle had no respect for the boundaries between scientific disciplines, which were artificial social constructs that often stood in the way of a proper comprehension of the cosmos. The Universe does not respect the differences between physics, chemistry and biology, he would say, and his career in astronomy progressively embraced all these disciplines. With meticulous attention to detail he proceeded to master whatever discipline was needed in order to explore the Universe. Nor was Hoyle ever daunted by the enormous difficulty of some of the problems he tackled. With resolute determination and a fearless independence of mind he devoted a lifetime to understanding the world in which we live.

Hoyle will also be remembered as one of the greatest popularisers of science in the 20th century, following in the distinguished traditions of H.G. Wells, James Jeans and Arthur Eddington. He had a rare gift of explaining complex scientific concepts in the simplest of terms, and in so doing he never failed to captivate huge audiences on radio and television, in public lectures as well as through his popular books.

In 1950 he gave an historic series of radio talks on the BBC Third Programme (which was published the following year as a book, The Nature of the Universe). Millions of listeners and readers of Hoyle the world over admit to having been enticed into science by the power of his arguments and his inimitable style of exposition. His more serious scientific work, meanwhile, served as an inspiration to three generations of astronomers. Hoyle taught us by his example to explore the world and search for truth objectively and fearlessly, without prejudice, being guided only by the compelling trajectory of logic.

Hoyle often condemned the enormous social pressures that are brought to bear on scientists nowadays to conform. He sneered at the modern practices of peer review and science umpiring conducted by journals, declaring them to be an invitation to unconstructive conformism, an impediment to the progress of science. For expressing such forthright views, he was criticised by the scientific establishment and he made many enemies.

Hoyle's researches during the period 1945-72 were carried out at Cambridge University, where in 1958 he became Plumian Professor of Astronomy and subsequently the founder director of the Institute of Astronomy. He retired from this position in 1972, then continued to work actively in many areas of astronomy, attached loosely to a variety of universities, principally, from 1975, to University College, Cardiff.

Although he might be best remembered for his more daring scientific pursuits -- his unorthodox cosmology and more recently his support of panspermia -- there is scarcely an area of astronomy that has not been touched in some way by Hoyle's genius.

Hoyle's work on nucleosynthesis in collaboration with William A. Fowler and Geoffrey and Margaret Burbidge led to our present-day understanding of the origin of chemical elements in stars. It was Hoyle's original prediction of the presence of an excited state of the nucleus of the atom Carbon via his studies of the structure and evolution of stars that heralded a long and profitable collaboration with the Caltech nuclear physicist Willy Fowler.

In the 1940s Hoyle collaborated with R.A. Lyttleton and Hermann Bondi in laying the foundations of the theory of accretion -- the mechanism by which stars "suck in" nearby interstellar matter. A little later, he had worked out a theory of how interstellar clouds can break up into fragments to form stars, which again forms the basis of all modern theories of the formation of stars.

In the 1950s Hoyle, together with Bondi and Thomas Gold, propounded the Steady State Theory of the Universe. This was to challenge the then fashionable cosmological theory that supposed the Universe to begin with the explosion of a super atom some 15 billion years ago. Hoyle and his colleagues found such a theory philosophically unsatisfactory -- it could not, for instance, answer the question: what was there before the initial explosion? In order to denigrate the theory that he disliked Hoyle coined the term "Big Bang Cosmology", a term that has stuck for nearly half a century.

Throughout the 1950s and 1960s a fierce battle raged between the proponents of the two schools of cosmology: Steady State vs Big Bang. I was privileged to come to Cambridge as Hoyle's research student in 1960 and witnessed the scientific-sociological struggle between two rival camps first hand. With the flimsiest of evidence, particularly from studies of radio galaxies by Martin Ryle at Cambridge, each side was making strong claims for itself and the debate turned bitter and acrimonious at times.

The discovery of a background of microwave radiation in the Universe by A. Penzias and R. Wilson in 1964 tipped the balance strongly against the original version of the Steady State Universe, the radiation being explained as the cooled-off relic of the heat of the Big Bang. Hoyle, together with myself and Jayant Narlikar, did not accept these data to be a defeat for the Steady State, and have indicated many reasonable ways in which the background radiation can be produced without a Big Bang. For instance, the light of galaxies could be absorbed by iron whiskers expelled from supernovae and these whiskers then emit microwaves. In a recent book by Hoyle, with Narlikar and Burbidge, A Different Approach to Cosmology (1999), a revised form of the Steady State Theory, known as the "Quasi-Steady State Cosmology", is shown to be fully consistent with all the astronomical observation.

In 1962 Hoyle and I sought to understand the nature of cosmic dust, those gigantic clouds of obscuring matter that could be seen in photographs of the Milky Way. At the time we began our researches the generally accepted view was that these cosmic dust particles are similar to the micron-sized ice crystals found in the cumulus clouds of the Earth's atmosphere. We challenged this paradigm by showing that carbon particles are a more plausible model for the dust, and over the years astronomers have come to accept this carbon (graphite) grain theory as being close to proven.

We ourselves moved on from inorganic carbon dust to organic dust and finally to biological particles for the composition of the interstellar dust. In 1977 Hoyle and I argued that the origin of life on Earth must have involved the importation of viable cells from space, thereby challenging another Holy Grail of science, "The Primordial Soup Theory", for the origins of life. At first this theory, known as "panspermia", was regarded as heretical, but new evidence from many directions appears be moving towards a vindication of this point of view.

Last month the first evidence of microbes at the edge of the Earth's atmosphere at 41km was presented in a paper to a meeting of the Society of Optical Engineering. Hoyle himself was unable to see the final form of this paper although he was a co-author and mentor of this work. Now, 34 years on, some form of panspermia theory of life's origins appears to be gaining ground.

Perhaps the most controversial aspect of Hoyle's work involves the ideas of pathogenic bacteria and viruses arriving from space, and that the evolution of life may be directed from outside. This work has raised fierce hostility in some circles.

Hoyle was sometimes unfairly presented as one who courted controversy for the sake of it. My knowledge of Hoyle as a friend and colleague convinces me that this criticism is unfounded. He was always the most charitable of people and he never failed to acknowledge debts to earlier work or to others wherever they were due. In his more unorthodox scientific ventures he simply pursued the path that logic led him, or so he thought. Sometimes his intuition may have been wrong, but more often he turned out to be right. On the biggest questions of the origin of the Universe and the origin of life the last word has surely not been said, and Hoyle would have been the first to admit that.

Fred Hoyle was born in 1915 in Bingley, and educated at Bingley Grammar School and Emmanuel College, Cambridge, where he studied Mathematics. In 1939 he was elected a Fellow of St John's College, Cambridge, and in 1945, following Admiralty Service during the Second World War, joined the Cambridge University Department of Mathematics as an Assistant Lecturer.

Although he paid little attention to accolades, awards and approbations, he received many honours and distinctions. He was awarded the UN Kalinga Prize for the popularisation of science in 1968. In 1997 the Swedish Academy of Sciences awarded him the Crafoord Prize designed to honour work in fields that were not eligible for the Nobel Prize. In 1957 he became a Fellow of the Royal Society, in 1969 a Foreign Associate of the US National Academy of Sciences, and in 1971 the President of the Royal Astronomical Society. He was knighted in 1972. He was an Honorary Fellow at both St John's College and Emmanuel College, and an Honorary Professor at Cardiff University since 1975.

There are very few things stranger in the world of literature than a scientist having fun. And, of all the scientists who wrote novels in the 20th century, few were stranger -- or had more fun -- than Fred Hoyle.

His scientific credentials may have been impeccable, and many readers were fooled by them to read his science-fiction tales as expositions of how to think extremely hard; but underneath the deadpan, rapid-fire surface of novels like Fifth Planet (1959), A for Andromeda (1962, with John Elliot), or In Deepest Space (1974), could be discovered the buried signposts of a genuine trickster at work.

The Black Cloud (1957), which was Hoyle's first novel, has been understood as an attempt to dramatise the thought processes and procedures of a scientist at work. It is, in fact, like all its successors, a dramatic exercise in escaping the tension and rigour of those thought processes: as we learn, a very large black cloud has drifted from out of nowhere into our solar system, and has taken up residency around the Sun. In the nick of time, an adventurous scientist discovers that the cloud is (or has) a brain, and talks to it. The intensity of this experience drives him insane, but the rest of us are saved.

In Ossian's Ride (1959) another unsedentary scientist rollicks about Ireland, chasing after dire knowledge. When he reaches Dublin, he finds it has been transformed into a vast skyscraper-dominated metropolis. In the end, this cure for Ireland's woes is revealed to have been inspired by aliens exiled on our planet. Hoyle's hero enthusiastically joins in.

It is impossible to know for certain how serious Hoyle was about this solution to the mud and ire of the real world and its problems. In one of the last of his 15 novels to show genuine exuberance -- The Inferno (1973), written with his son Geoffrey -- the old gay brutality remains intact. Waves of radiation are about to make life on most of Earth impossible. The governments of the world (as always in Hoyle's fiction) are both incompetent and corrupt. The scientist who has discovered the radiation becomes dictator of those who manage to survive.

These tales may have been meant simply as mind games, intended to divert author and audience from a frustratingly complicated world. But, whether or not they were froth on the daydreams of a hard-nosed physicist whose real-life experiences were not entirely jovial, Hoyle's science-fiction novels convey a surreal pugnacity of argument, a deep and sometimes hilarious oddness of mien, that makes them instantly recognisable. They are brilliant, uncouth, gadfly, impertinent, joyful; but more than anything -- more than almost any other science fiction ever written -- they are strange. They are from another planet.